sorry for the confusion!

Did more test and found that the section of code doesn't only execute once when multiple mouse clicks were simulated.

Here is what happened: I use a program to enumerate the windows on the desktop, and when I see some specific window, I will simulate a mouse click to that window. However, sometimes the window can be found during enumeration but it doesn't really "exist" --- means it is not visible and you can't click it. The mouse click will go to the window "behind" the invisible one. That's why I felt like there are more mouse clicks than it should.